With frequent occurrence of cyanobacterial blooms in recent years, cyanotoxins have become a great threat to aquatic animals, livestock, and human health. Among these toxins, microcystins (MCs) are the most common and dangerous hepatotoxins, which intensely inhibit protein phosphatases 1 and 2A in liver, leading to hepatic damage. In this paper, acute toxicity experiments were conducted in crucian carp and Japanese white rabbit to exame tissue distribution of MCs, using liquid chromatography coupled with mass spectrometry (HPLC-MS). Combining previous studies, we provided more information on toxicity of MCs by comparing tisuuse distribution of MCs between fish and mammal. The main results and conclusions were summarized as follows:
Crucian carp were injected intraperitoneally with MC extract at two doses (200 and 50 μg MC-LReq./kg bw), and MC concentrations in various tissues were analyzed at 1, 3, 12, 24, 48 and 144 h postinjection, using LC-MS. MCs entered into the circulatory system rapidly after intraperitoneal injection, and were transported to various organs, which subsequently resulted in different levels of MCs in various tissues. In all samples with detectable toxins, MC-RR was dominant wheras MC-LR contents were extremely low or even undetectable, except in the liver sample at a dose of 200 µg/kg (11-597 ng/g DW). Such differences between the distribution of MC-RR and MC-LR in fish tissues might be due to organ specificity of MCs. In both dose groups, the highest concentrations of MCs (MC-RR + MC-LR) were found in blood at 1 h post-injection, 3757 ng/g DW (200 µg/kg dose group) and 270 ng/g DW (50 µg/kg dose group), respectively. MC-RR content in kidney was negatively correlated with that in blood in both dose groups, suggesting that blood was important in the transportation of MC-RR to kidney for excretion. After injection, liver to body weight ratio increased in crucian carp in both dose groups, especially in the 50 µg/kg dose group, which might be due to hydropic degeneration in liver. High depuration rate of MCs was observed in liver: after 48 h, 96.3% (200 µg/kg dose group) and 85.7% (50 µg/kg dose group) of the absorbed toxins were cleared. MCs accumulated in heart, kidney, gonad and brain at different levels, suggesting MCs might be toxic to these organs.
Acute toxicity experiment in Japanese white rabbit: Japanese white rabbit were injected intraperitoneally with MC extract at two doses (50 and 12.5 μg MC-LReq./kg bw), and MC concentrations in various tissues were analyzed at 1, 3, 12, 24, and 48 h postinjection, using LC-MS. When rabbits were treated with 50 μg MC-LReq./kg bw via intraperitoneal injection, over half of the treated rabbits died at about 3 h post-injection, suggesting intense toxicity of MC to rabbit. MC contents in blood were very low in both dose groups, equal to only 0.02%-0.40% of the injected dose. In the 50 µg/kg dose group, the highest concentration of MCs was found in kidney, 62-158 ng/g DW, followed by liver, 54-82 ng/g DW. In the 12.5 µg/kg dose group, the highest concentration of MCs (MC-RR + MC-LR) was found in liver (15-65 ng/g DW) with a significant increase at 48 h compared with that at 1 h, suggesting that it was difficult for rabbit to clear up MCs in liver. Relative high MC content was observed in gastrointestinal tract and no decreace trend was showed in MC content in gallbladder and spleen, which might be attributed to the recirculation of adsorbed MC. MCs accumulated in lung, kidney and brain at different levels, suggesting that MCs might be toxic to these organs.